diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 8eac4542..a27663f8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -19,13 +19,14 @@ jobs:
       matrix:
         ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest, windows-latest ]
-        experimental: [false]
-        exclude:
-          - { ruby: head, os: windows-latest }
         include:
-          - { ruby: head, os: windows-latest, experimental: true }
+          - { ruby: head,                                 experimental: true }
+          # - { ruby: jruby,            os: ubuntu-latest,  experimental: true }
+          - { ruby: jruby-head,       os: ubuntu-latest,  experimental: true }
+          # - { ruby: truffleruby,      os: ubuntu-latest,  experimental: true }
+          - { ruby: truffleruby-head, os: ubuntu-latest,  experimental: true }
     runs-on: ${{ matrix.os }}
-    continue-on-error: ${{ matrix.experimental }}
+    continue-on-error: ${{ matrix.experimental || false }}
     timeout-minutes: 15
     steps:
     - uses: actions/checkout@v4
@@ -40,7 +41,8 @@ jobs:
       timeout-minutes: 5 # _should_ finish in under a minute
 
     - uses: joshmfrankel/simplecov-check-action@main
-      if: matrix.os == 'ubuntu-latest' && github.event_name != 'pull_request'
+      if: ${{ matrix.os == 'ubuntu-latest' && github.event_name != 'pull_request' &&
+        !startsWith(matrix.ruby, 'truffleruby') && !startsWith(matrix.ruby, 'jruby') }}
       with:
         check_job_name: "SimpleCov - ${{ matrix.ruby }}"
         minimum_suite_coverage: 90
diff --git a/lib/net/imap.rb b/lib/net/imap.rb
index c9a1e66d..c72992a3 100644
--- a/lib/net/imap.rb
+++ b/lib/net/imap.rb
@@ -1116,8 +1116,8 @@ def tls_verified?; @tls_verified end
     #
     # Related: #logout, #logout!
     def disconnect
+      in_logout_state = try_state_logout?
       return if disconnected?
-      state_logout!
       begin
         begin
           # try to call SSL::SSLSocket#io.
@@ -1131,11 +1131,15 @@ def disconnect
       rescue Exception => e
         @receiver_thread.raise(e)
       end
-      @receiver_thread.join
       synchronize do
         @sock.close
       end
+      @receiver_thread.join
       raise e if e
+    ensure
+      # Try again after shutting down the receiver thread.  With no reciever
+      # left to wait for, any remaining locks should be _very_ brief.
+      state_logout! unless in_logout_state
     end
 
     # Returns true if disconnected from the server.
@@ -3062,8 +3066,8 @@ def idle(timeout = nil, &response_handler)
             raise @exception || Net::IMAP::Error.new("connection closed")
           end
         ensure
+          remove_response_handler(response_handler)
           unless @receiver_thread_terminating
-            remove_response_handler(response_handler)
             put_string("DONE#{CRLF}")
             response = get_tagged_response(tag, "IDLE", idle_response_timeout)
           end
@@ -3346,8 +3350,6 @@ def start_receiver_thread
       rescue Exception => ex
         @receiver_thread_exception = ex
         # don't exit the thread with an exception
-      ensure
-        state_logout!
       end
     end
 
@@ -3429,6 +3431,8 @@ def receive_responses
           @idle_done_cond.signal
         end
       end
+    ensure
+      state_logout!
     end
 
     def get_tagged_response(tag, cmd, timeout = nil)
@@ -3791,15 +3795,29 @@ def state_selected!
     end
 
     def state_unselected!
-      state_authenticated! if connection_state.to_sym == :selected
+      synchronize do
+        state_authenticated! if connection_state.to_sym == :selected
+      end
     end
 
     def state_logout!
+      return true if connection_state in [:logout, *]
       synchronize do
+        return true if connection_state in [:logout, *]
         @connection_state = ConnectionState::Logout.new
       end
     end
 
+    # don't wait to aqcuire the lock
+    def try_state_logout?
+      return true if connection_state in [:logout, *]
+      return false unless acquired_lock = mon_try_enter
+      state_logout!
+      true
+    ensure
+      mon_exit if acquired_lock
+    end
+
     def sasl_adapter
       SASLAdapter.new(self, &method(:send_command_with_continuations))
     end
diff --git a/lib/net/imap/data_lite.rb b/lib/net/imap/data_lite.rb
index 5b96c873..733bd946 100644
--- a/lib/net/imap/data_lite.rb
+++ b/lib/net/imap/data_lite.rb
@@ -24,10 +24,56 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
 
-
 module Net
   class IMAP
-    data_or_object = RUBY_VERSION >= "3.2.0" ? ::Data : Object
+
+    # :nocov:
+    # Skip coverage: how much of the file runs depends on the engine version.
+
+    # Test whether RUBY_ENGINE has sufficient support for ::Data.
+    # TODO: golf this down to the bare minimum that's failing.
+    data_or_object = ::Object
+    if defined?(::Data) && ::Data.respond_to?(:define)
+      begin
+        class TestData < ::Data
+          def self.YAML(data)
+            coder = Struct.new(:map).new(data)
+            data = self.allocate
+            data.init_with(coder)
+            data
+          end
+          def init_with(coder) initialize(**coder.map.transform_keys(&:to_sym)) end
+          def deconstruct; [:ok, *super] end
+        end
+
+        class TestDataDefine < TestData.define(:str, :bool)
+          def initialize(str: nil, bool: nil)
+            str  => String       | nil; str  = -str if str
+            bool => true | false | nil; bool = !!bool
+            super
+          end
+        end
+
+        test_init = TestDataDefine.YAML({"str" => "str"})
+        test_empty = TestData.define[]
+
+        if test_init.deconstruct != [:ok, "str", false]
+          raise "subclassing misbehaves"
+        elsif test_empty.deconstruct != [:ok]
+          raise "can't define empty"
+        end
+        data_or_object = ::Data
+      rescue => ex
+        warn "Insufficient implementation of Data: %s (%s) for %s %s" % [
+          ex, ex.class, RUBY_ENGINE, RUBY_ENGINE_VERSION,
+        ]
+        data_or_object = ::Object
+      ensure
+        remove_const :TestData       if const_defined?(:TestData)
+        remove_const :TestDataDefine if const_defined?(:TestDataDefine)
+      end
+    end
+
     class DataLite < data_or_object
       def encode_with(coder) coder.map = to_h.transform_keys(&:to_s)        end
       def init_with(coder) initialize(**coder.map.transform_keys(&:to_sym)) end
@@ -37,9 +83,7 @@ def init_with(coder) initialize(**coder.map.transform_keys(&:to_sym)) end
   end
 end
 
-# :nocov:
-# Need to skip test coverage for the rest, because it isn't loaded by ruby 3.2+.
-return if RUBY_VERSION >= "3.2.0"
+return unless Net::IMAP::DataLite.superclass == Object
 
 module Net
   class IMAP
diff --git a/test/lib/helper.rb b/test/lib/helper.rb
index 3128c533..a4f53939 100644
--- a/test/lib/helper.rb
+++ b/test/lib/helper.rb
@@ -1,31 +1,34 @@
-require "simplecov"
-
-# Cannot use ".simplecov" file: simplecov-json triggers a circular require.
-require "simplecov-json"
-SimpleCov.formatters = SimpleCov::Formatter::MultiFormatter.new([
-  SimpleCov::Formatter::HTMLFormatter,
-  SimpleCov::Formatter::JSONFormatter,
-])
-
-SimpleCov.start do
-  command_name "Net::IMAP tests"
-  enable_coverage  :branch
-  primary_coverage :branch
-  enable_coverage_for_eval
-
-  add_filter "/test/"
-  add_filter "/rakelib/"
-
-  add_group "Parser", %w[lib/net/imap/response_parser.rb
-                         lib/net/imap/response_parser]
-  add_group "Config", %w[lib/net/imap/config.rb
-                         lib/net/imap/config]
-  add_group "SASL", %w[lib/net/imap/sasl.rb
-                       lib/net/imap/sasl
-                       lib/net/imap/authenticators.rb]
-  add_group "StringPrep", %w[lib/net/imap/stringprep.rb
-                             lib/net/imap/stringprep]
+if RUBY_ENGINE == "ruby" # C Ruby only
+  require "simplecov"
+
+  # Cannot use ".simplecov" file: simplecov-json triggers a circular require.
+  require "simplecov-json"
+  SimpleCov.formatters = SimpleCov::Formatter::MultiFormatter.new([
+    SimpleCov::Formatter::HTMLFormatter,
+    SimpleCov::Formatter::JSONFormatter,
+  ])
+
+  SimpleCov.start do
+    command_name "Net::IMAP tests"
+    enable_coverage  :branch
+    primary_coverage :branch
+    enable_coverage_for_eval
+
+    add_filter "/test/"
+    add_filter "/rakelib/"
+
+    add_group "Parser", %w[lib/net/imap/response_parser.rb
+                          lib/net/imap/response_parser]
+    add_group "Config", %w[lib/net/imap/config.rb
+                          lib/net/imap/config]
+    add_group "SASL", %w[lib/net/imap/sasl.rb
+                        lib/net/imap/sasl
+                        lib/net/imap/authenticators.rb]
+    add_group "StringPrep", %w[lib/net/imap/stringprep.rb
+                              lib/net/imap/stringprep]
+  end
 end
+
 require "test/unit"
 require "core_assertions"
 
@@ -54,4 +57,44 @@ def assert_pattern
     end
   end
 
+  def pend_if(condition, *args, &block)
+    if condition
+      pend(*args, &block)
+    else
+      block.call if block
+    end
+  end
+
+  def pend_unless(condition, *args, &block)
+    if condition
+      block.call if block
+    else
+      pend(*args, &block)
+    end
+  end
+
+  def omit_unless_cruby(msg = "test omitted for non-CRuby", &block)
+    omit_unless(RUBY_ENGINE == "ruby", msg, &block)
+  end
+
+  def omit_if_truffleruby(msg = "test omitted on TruffleRuby", &block)
+    omit_if(RUBY_ENGINE == "truffleruby", msg, &block)
+  end
+
+  def omit_if_jruby(msg = "test omitted on JRuby", &block)
+    omit_if(RUBY_ENGINE == "jruby", msg, &block)
+  end
+
+  def pend_unless_cruby(msg = "test is pending for non-CRuby", &block)
+    pend_unless(RUBY_ENGINE == "ruby", msg, &block)
+  end
+
+  def pend_if_truffleruby(msg = "test is pending on TruffleRuby", &block)
+    pend_if(RUBY_ENGINE == "truffleruby", msg, &block)
+  end
+
+  def pend_if_jruby(msg = "test is pending on JRuby", &block)
+    pend_if(RUBY_ENGINE == "jruby", msg, &block)
+  end
+
 end
diff --git a/test/net/imap/test_config.rb b/test/net/imap/test_config.rb
index aa9ed5e7..20f1f3f9 100644
--- a/test/net/imap/test_config.rb
+++ b/test/net/imap/test_config.rb
@@ -270,10 +270,15 @@ def duck.to_r   = 1/11111
   test "#freeze" do
     config = Config.new(open_timeout: 1)
     config.freeze
-    assert_raise FrozenError do
-      config.open_timeout = 2
+    assert config.frozen?
+    assert config.__send__(:data).frozen?
+    pend_if_truffleruby "https://github.com/oracle/truffleruby/issues/3850" do
+      assert_raise FrozenError do
+        config.open_timeout = 2
+        assert_equal 1, config.open_timeout
+      end
+      assert_equal 1, config.open_timeout
     end
-    assert_same 1, config.open_timeout
   end
 
   test "#dup" do
@@ -302,10 +307,14 @@ def duck.to_r   = 1/11111
     original.freeze
     copy = original.clone
     assert copy.frozen?
-    assert_raise FrozenError do
-      copy.open_timeout = 2
+    assert copy.__send__(:data).frozen?
+    pend_if_truffleruby "https://github.com/oracle/truffleruby/issues/3850" do
+      assert_raise FrozenError do
+        copy.open_timeout = 2
+        assert_equal 1, copy.open_timeout
+      end
+      assert_equal 1, copy.open_timeout
     end
-    assert_equal 1, copy.open_timeout
   end
 
   test "#inherited? and #reset(attr)" do
diff --git a/test/net/imap/test_data_lite.rb b/test/net/imap/test_data_lite.rb
index 54c57b89..6ad724ba 100644
--- a/test/net/imap/test_data_lite.rb
+++ b/test/net/imap/test_data_lite.rb
@@ -154,6 +154,14 @@ def test_inspect
       end
 
       def test_recursive_inspect
+        if Data.superclass == ::Object
+          omit_if_truffleruby "TruffleRuby: format('%p', nil) returns '': " \
+                              "https://github.com/oracle/truffleruby/issues/3846"
+        else
+          omit_if_truffleruby "TruffleRuby: Data#inspect has stack overflow: " \
+                              "https://github.com/oracle/truffleruby/issues/3847"
+        end
+
         klass = Data.define(:value, :head, :tail) do
           def initialize(value:, head: nil, tail: nil)
             case tail
@@ -183,6 +191,7 @@ def initialize(value:, head: nil, tail: nil)
           " tail=#<data value=3, head=#{seen}," \
           " tail=#<data value=4, head=#{seen}," \
           " tail=nil>>>>",
+          # TODO: JRuby's Data fails on the next line
           list.inspect
         )
 
@@ -196,6 +205,7 @@ def initialize(value:, head: nil, tail: nil)
           " tail=#<data DoubleLinkList value=3, head=#{seen}," \
           " tail=#<data DoubleLinkList value=4, head=#{seen}," \
           " tail=nil>>>>",
+          # TODO: JRuby's Data fails on the next line
           list.inspect
         )
       ensure
@@ -340,6 +350,47 @@ def other
         assert_equal("test", data.name)
         assert_equal("other", data.other)
       end
+
+      class Abstract < Data
+      end
+
+      class Inherited < Abstract.define(:foo)
+      end
+
+      def test_subclass_can_create
+        # TODO: JRuby's Data fails all of these
+        assert_equal 1, Inherited[1]    .foo
+        assert_equal 2, Inherited[foo: 2].foo
+        assert_equal 3, Inherited.new(3).foo
+        assert_equal 4, Inherited.new(foo: 4).foo
+      end
+
+      class AbstractWithClassMethod < Data
+        def self.inherited_class_method; :ok end
+      end
+
+      class InheritsClassMethod < AbstractWithClassMethod.define(:foo)
+      end
+
+      def test_subclass_class_method
+        # TODO: JRuby's Data fails on the next line
+        assert_equal :ok, InheritsClassMethod.inherited_class_method
+      end
+
+      class AbstractWithOverride < Data
+        def deconstruct; [:ok, *super] end
+      end
+
+      class InheritsOverride < AbstractWithOverride.define(:foo)
+      end
+
+      def test_subclass_override_deconstruct
+        # TODO: JRuby's Data fails on the next line
+        data = InheritsOverride[:foo]
+        # TODO: TruffleRuby's Data fails on the next line
+        assert_equal %i[ok foo], data.deconstruct
+      end
+
     end
   end
 end
diff --git a/test/net/imap/test_deprecated_client_options.rb b/test/net/imap/test_deprecated_client_options.rb
index ceb290dd..70999a5b 100644
--- a/test/net/imap/test_deprecated_client_options.rb
+++ b/test/net/imap/test_deprecated_client_options.rb
@@ -55,6 +55,7 @@ class InitializeTests < DeprecatedClientOptionsTest
     end
 
     test "Convert deprecated usessl (= true) and certs, with warning" do
+      omit_if_jruby "SSL tests don't work yet"
       run_fake_server_in_thread(implicit_tls: true) do |server|
         certs = server.config.tls[:ca_file]
         assert_deprecated_warning(/Call Net::IMAP\.new with keyword/i) do
@@ -71,6 +72,7 @@ class InitializeTests < DeprecatedClientOptionsTest
     end
 
     test "Convert deprecated usessl (= true) and verify (= false), with warning" do
+      omit_if_jruby "SSL tests don't work yet"
       run_fake_server_in_thread(implicit_tls: true) do |server|
         assert_deprecated_warning(/Call Net::IMAP\.new with keyword/i) do
           with_client("localhost", server.port, true, nil, false) do |client|
@@ -102,6 +104,7 @@ class InitializeTests < DeprecatedClientOptionsTest
 
   class StartTLSTests < DeprecatedClientOptionsTest
     test "Convert obsolete options hash to keywords" do
+      omit_if_jruby "SSL tests don't work yet"
       with_fake_server(preauth: false) do |server, imap|
         imap.starttls(ca_file: server.config.tls[:ca_file], min_version: :TLS1_2)
         assert_equal(
@@ -114,6 +117,7 @@ class StartTLSTests < DeprecatedClientOptionsTest
     end
 
     test "Convert deprecated certs, verify with warning" do
+      omit_if_jruby "SSL tests don't work yet"
       with_fake_server(preauth: false) do |server, imap|
         assert_deprecated_warning(/Call Net::IMAP#starttls with keyword/i) do
           imap.starttls(server.config.tls[:ca_file], false)
diff --git a/test/net/imap/test_fetch_data.rb b/test/net/imap/test_fetch_data.rb
index bcbbf50c..e51484bc 100644
--- a/test/net/imap/test_fetch_data.rb
+++ b/test/net/imap/test_fetch_data.rb
@@ -14,8 +14,10 @@ def fetch_data_class
   end
 
   test "#uid" do
-    data = Net::IMAP::FetchData.new(22222, "UID" => 54_321)
-    assert_equal 54_321, data.uid
+    pend_if_truffleruby do
+      data = Net::IMAP::FetchData.new(22222, "UID" => 54_321)
+      assert_equal 54_321, data.uid
+    end
   end
 end
 
@@ -25,20 +27,22 @@ def fetch_data_class
   end
 
   test "#seqno does not exist" do
-    data = Net::IMAP::UIDFetchData.new(22222)
+    data = pend_if_jruby { Net::IMAP::UIDFetchData.new(22222) } or next
     assert_raise NoMethodError do
       data.seqno
     end
   end
 
   test "#uid replaces #seqno" do
-    data = Net::IMAP::UIDFetchData.new(22222)
+    data = pend_if_jruby { Net::IMAP::UIDFetchData.new(22222) } or next
     assert_equal 22222, data.uid
   end
 
   test "#initialize warns when uid differs from attr['UID']" do
-    assert_warn(/UIDs do not match/i) do
-      Net::IMAP::UIDFetchData.new(22222, "UID" => 54_321)
+    pend_if_truffleruby do
+      assert_warn(/UIDs do not match/i) do
+        Net::IMAP::UIDFetchData.new(22222, "UID" => 54_321)
+      end
     end
   end
 
diff --git a/test/net/imap/test_imap.rb b/test/net/imap/test_imap.rb
index dd955b8d..f7037f95 100644
--- a/test/net/imap/test_imap.rb
+++ b/test/net/imap/test_imap.rb
@@ -28,6 +28,7 @@ def teardown
 
   if defined?(OpenSSL::SSL::SSLError)
     def test_imaps_unknown_ca
+      omit_if_jruby "SSL tests don't work yet"
       assert_raise(OpenSSL::SSL::SSLError) do
         imaps_test do |port|
           begin
@@ -42,6 +43,7 @@ def test_imaps_unknown_ca
     end
 
     def test_imaps_with_ca_file
+      omit_if_jruby "SSL tests don't work yet"
       # Assert verified *after* the imaps_test and assert_nothing_raised blocks.
       # Otherwise, failures can't logout and need to wait for the timeout.
       verified, imap = :unknown, nil
@@ -69,6 +71,7 @@ def test_imaps_with_ca_file
     end
 
     def test_imaps_verify_none
+      omit_if_jruby "SSL tests don't work yet"
       # Assert verified *after* the imaps_test and assert_nothing_raised blocks.
       # Otherwise, failures can't logout and need to wait for the timeout.
       verified, imap = :unknown, nil
@@ -96,6 +99,7 @@ def test_imaps_verify_none
     end
 
     def test_imaps_post_connection_check
+      omit_if_jruby "SSL tests don't work yet"
       assert_raise(OpenSSL::SSL::SSLError) do
         imaps_test do |port|
           # server_addr is different from the hostname in the certificate,
@@ -110,6 +114,7 @@ def test_imaps_post_connection_check
 
   if defined?(OpenSSL::SSL)
     def test_starttls_unknown_ca
+      omit_if_jruby "SSL tests don't work yet"
       omit "This test is not working with Windows" if RUBY_PLATFORM =~ /mswin|mingw/
 
       imap = nil
@@ -130,6 +135,7 @@ def test_starttls_unknown_ca
     end
 
     def test_starttls
+      omit_if_jruby "SSL tests don't work yet"
       initial_verified, initial_ctx, initial_params = :unknown, :unknown, :unknown
       imap = nil
       starttls_test do |port|
@@ -154,6 +160,7 @@ def test_starttls
     end
 
     def test_starttls_stripping
+      omit_if_jruby "SSL tests don't work yet"
       imap = nil
       starttls_stripping_test do |port|
         imap = Net::IMAP.new("localhost", :port => port)
@@ -512,6 +519,7 @@ def test_connection_closed_during_idle
   end
 
   def test_connection_closed_without_greeting
+    omit_if_jruby "???"
     server = create_tcp_server
     port = server.addr[1]
     h = {
diff --git a/test/net/imap/test_imap_capabilities.rb b/test/net/imap/test_imap_capabilities.rb
index ca83a20f..16ad1922 100644
--- a/test/net/imap/test_imap_capabilities.rb
+++ b/test/net/imap/test_imap_capabilities.rb
@@ -139,6 +139,7 @@ def teardown
 
   if defined?(OpenSSL::SSL::SSLError)
     test "#capabilities caches greeting capabilities (implicit TLS)" do
+      omit_if_jruby
       with_fake_server(preauth: false, implicit_tls: true) do |server, imap|
         assert imap.capabilities_cached?
         assert_equal %w[IMAP4REV1 AUTH=PLAIN], imap.capabilities
@@ -151,6 +152,7 @@ def teardown
 
     test "#capabilities cache is cleared after #starttls" do
       with_fake_server(preauth: false, cleartext_auth: false) do |server, imap|
+        omit_if_jruby
         assert imap.capabilities_cached?
         assert imap.capable? :IMAP4rev1
         refute imap.auth_capable? "plain"
@@ -204,6 +206,7 @@ def teardown
 
   # TODO: should we warn about this?
   test "#capabilities cache IGNORES tagged OK response to STARTTLS" do
+    omit_if_jruby
     with_fake_server(preauth: false) do |server, imap|
       server.on "STARTTLS" do |cmd|
         cmd.done_ok code: "[CAPABILITY IMAP4rev1 AUTH=PLAIN fnord]"
diff --git a/test/net/imap/test_imap_connection_state.rb b/test/net/imap/test_imap_connection_state.rb
index 41f4f5bf..bb990eb4 100644
--- a/test/net/imap/test_imap_connection_state.rb
+++ b/test/net/imap/test_imap_connection_state.rb
@@ -26,6 +26,7 @@ class ConnectionStateTest < Test::Unit::TestCase
   end
 
   test "#deconstruct" do
+    # TODO: TruffleRuby's Data fails these
     assert_equal [:not_authenticated], NotAuthenticated[].deconstruct
     assert_equal [:authenticated],     Authenticated[]   .deconstruct
     assert_equal [:selected],          Selected[]        .deconstruct
@@ -33,6 +34,7 @@ class ConnectionStateTest < Test::Unit::TestCase
   end
 
   test "#deconstruct_keys" do
+    # TODO: TruffleRuby's Data fails these
     assert_equal({symbol: :not_authenticated}, NotAuthenticated[].deconstruct_keys([:symbol]))
     assert_equal({symbol: :authenticated},     Authenticated[]   .deconstruct_keys([:symbol]))
     assert_equal({symbol: :selected},          Selected[]        .deconstruct_keys([:symbol]))
diff --git a/test/net/imap/test_response_reader.rb b/test/net/imap/test_response_reader.rb
index cec6768e..77f506f6 100644
--- a/test/net/imap/test_response_reader.rb
+++ b/test/net/imap/test_response_reader.rb
@@ -79,9 +79,11 @@ def literal(str) = "{#{str.bytesize}}\r\n#{str}"
     client.config.max_response_size = 10
     io = StringIO.new(barely_over)
     rcvr = Net::IMAP::ResponseReader.new(client, io)
-    assert_raise Net::IMAP::ResponseTooLargeError do
-      result = rcvr.read_response_buffer
-      flunk "Got result: %p" % [result]
+    pend_if_truffleruby do
+      assert_raise Net::IMAP::ResponseTooLargeError do
+        result = rcvr.read_response_buffer
+        flunk "Got result: %p" % [result]
+      end
     end
   end